In the Punjab, tomatoes are grated to make a puree. Don't be
tempted to use ready-prepared tomato puree instead of fresh.

The spice combinations in garam masala vary in different parts of
India.

In the Punjab this one which you can try making yourself is
common: 5 tbsps coriander seeds, 3 tbsps cumin seeds, 2 1/2 tbsps
black peppercorns, 2 1/2 black cardamom seeds, 2 in cinnamon stick,
4-5 cloves, 1/6 nutmeg. Put the coriander and the cumin into a
cast-iron frying-pan over a medium heat.

Stir until lightly roasted. Allow to cool. Grind with the
remaining ingredients in a clean coffee grinder and store in a
tightly lidded jar.